Generally, steel used in various constructions like steel bridge and so on has increased in its number and size, and became important and indispensable material for the modern civilization. While, since these materials have serious fault like deterioration or corrosion by an environment in which they are used, their usage has lot of impediments. Particularly, metallic materials most of which are steel, reduced from stable natural metallic oxides (in rust form) by applying lots of energy to be a useful material for practical use, are unstable and have natural corrosive tendency to turn back to their more stable state.
Therefore, a corrosion loss of the metallic materials amounts to as much as 2-3% of the GNP in the western industrialized country according to the recent survey. A cost from the loss directly from the metal corrosion amounts to 250 billion dollars annually according to the 2002 US statistical data. Of course, if the indirect loss is counted such as suspension by corrosion related repair or stoppage of operation, decline of efficiency, reconstruction, burdensome design and so on, its economical loss would be enormous.
Further, since the corrosion problem related to the economical aspect may also lead to life casualties, it is important to recognize a seriousness of such corrosion problems.
Serious corrosion problems prevalent in most of the preexistent facilities and constructions due to negligence of such corrosion problems may bring on public criticism and are currently influencing a risk in safety to their peripheral regions. Moreover, despite this situation, the reality is, an importance of a basic technology which became a common sense in the developed country has not been recognized and, frequently, the basic technology is not considered in a design even in the recent major construction works.
Further, the steel bridges in Korea are being constructed in concrete with steel structure and the steel bridge is coated with a periodic rust resisting paint around most of the main members such as iron reinforcing rod, steel frame or bolt connecting part, welding connected part and so on predicted to be corroded from an initial stage of construction. Meanwhile, despite the above way of coating rust resisting paint, environmental conditions of these constructions became more various and severe by the pollution and the progress of industry, and the constructions cannot sustain their reasonable life spans but deteriorated and continuously cause damages from corrosion loss.
Further, a recent increase of corrosion factors of steel structures by construction of structures in oceanic environment and use of chloride material for removal of snow and the like is bringing out an importance of repair and maintenance of the steel structures, and requiring an economic and efficient management of them. As a life span of the paint coated film is considerably shorter than a life span year of the steel bridge, repainting should be achieved in an appropriate time in order to maintain a fair paint coated film state.
A conventional method of inspecting the paint coated film hereinabove referring to FIG. 1 includes: a storage step S101 that stores image information of deteriorated paint coated film of the steel bridge photographed by still picture or video in memory means;
a deteriorated area calculation step S102 that calculates a characteristic amount such as deteriorated area ratio occupied with faults like rust, scale and so on or images and the like from the photographed image information of the deteriorated paint coated film on the steel bridge after the storage step S101 and;
a deteriorated paint coated film of bridge extraction step S103 that extracts a bridge which brought out a premature or an abnormal deterioration of paint coated film by a remaining life span (time for repainting) based on evaluation for deteriorated paint coated film obtained by the calculated characteristic amount after the deterioration area calculation step S102 and a coated paint film deterioration curve (tendency of deterioration of paint coated film) obtained for every bridge as shown in FIG. 2.
Meanwhile, if the above conventional method of inspecting the paint coasted film is described more specifically, photographs stored in the memory means or image information of the deteriorated paint coated film of the steel images photographed in video are called, and a characteristic amount such as deteriorated area ratio occupied with faults like rust, scale and so on, and shape and the like is extracted. That is, if deteriorated region of the paint coated film (damaged part) such as rust, scale and the like is compared to its surrounded region of normal paint coated film, generally, the deteriorated region is relatively darker and its shape is schematically shown in FIG. 2A.
Even if the method of differentiation by an indicated brightness (the method that determines a darker part of a paint coated film as a deteriorated part and, a brighter part of it compared with a certain indicated brightness as a normal paint coated film part) to extract the deteriorating region from the above images is applied, it cannot obtain a result as good as that from a person's eye sight.
If the brightness does not reach the indicated brightness (critical value), the part is regarded as deteriorated part even if it is not a deteriorated part and, in the contrary, it may not be regarded as a deteriorated part if that part is brighter than the critical value even if it is a deteriorated part as shown in FIG. 2B.
Specifically, a maximum value filter process is performed to an input image of FIG. 2A. The maximum value filter process is a process converting a brightness of one point P in the image to the brightest brightness among its peripheral region. Darker points compared to their peripheral region in a range (filter size) are filled with deteriorated parts changed in brightness identical to their peripheral region (FIG. 2C). Meanwhile, a minimum value filter process is performed to an image of FIG. 2C. Contrary to the maximum value filter process, the minimum value filter process is a process converting a brightness of one point P in the image to the darkest brightness among its peripheral region.
The overall brighter image by the maximum value filter process may be restored back to its original brightness according to the above conversion. However, since a part recognized as a deteriorated part once undergone the maximum value filter process cannot be restored back to its original, an image extracted of only the deteriorated part (darker points compared to their peripheral regions) among the input image of FIG. 2A may be obtained (FIG. 2D). Accordingly, if an image is obtained from FIG. 2A distracted of FIG. 2D, it became an image of only deteriorated part without influenced by a brightness variation. Then, in case that there is a brightness variation in the image, a relatively dark region compared to its peripheral region at respective regions in the image is extracted and recognized as a deteriorated part.